Patent GB-505568-A (GB)
Title: Improvements in electric brakes
IPC: H02K49/04
Filed: 1937-11-12
Abstract: 505,568. Eddy-current brakes. LIST, H. Nov. 12, 1937, No. 31085. [Class 103 (i)] In eddy-current brakes for vehicles or other heavy duty, means are provided adapted to move responsively to the speed of the rotor of the brake throughout all or practically all of its speed range so that with fall of speed to a low speed there is comparatively little change in the braking effort. In Fig. 1, a copper disc a rotates between the poles b of an electromagnet c carried by a lever d pivoted at k and normally held by a spring f against a stop g. When the magnet is energized the lever is moved downwardly to a position dependent upon the speed, against the action of the spring by the action of the eddy currents in the disc thus reducing the effective field area of the magnet. The braking action may thus be maintained practically constant. The force and movement of the spring may be adjusted by the screw f<1> or by sliding the block e. A speed responsive device such as a centrifugal governor may be arranged to adjust the screw f<1> or block e to give a more nearly constant braking action. A weight may be substituted for the spring to ensure a constant loading in all positions of the lever. The magnet, instead of being mounted on a lever, may be displaceable on a stationary support by a centrifugal governor, to adjust the effective field area. In Fig. 2, an eddy current cylinder a extending into the gap between the poles of a stationary pot-magnet b and freely mounted upon the rotating shaft i is connected by oblique links l to a disc o splined on the shaft. When the brake is operative, the braking torque turns the cylinder relatively to the shaft thus compressing a spring n disposed between the cylinder and disc o, and withdrawing the cylinder until equilibrium is reached. The disc o abuts through a ball thrust bearing on a nut p by turhing which the initial compression of the spring can be adjusted. When the axis of the brake is vertical the spring may be replaced by the weight of the disc m secured to cylinder a. The links l may be dispensed with and the spring be secured to the cylinders and disc o so as to act in torsion. The links may be replaced by a screw-and-nut device for effecting the automatic compression of the spring. Fig. 4 shows such a device in which the magnet b is secured to the rotating shaft i to be braked. The eddy current cylinder a is secured to a cylinder m which is adapted to turn, under the influence of the braking torque, on a screwed member p, thus compressing the spring n. The member p screws for adjustment on a fixed member q<1>. The spring pressure may be automatically adjusted by connecting a centrifugal governor or other speed responsive device to the member p. In an arrangement for automatically adjusting the intensity of the field of the magnet a lever such as d, Fig. 1, carrying the magnet acts against a spring to vary the resistance of a carbon or other rheostat. The air gap may also be adjusted. To reduce the magnetic resistance of the gap pins of iron or other magnetic material may be distributed in the eddycurrent disc or cylinder. The cylinder a may be provided with a chamber u, Figs. 2, 4 through which cooling water is circulated, the liquid being conducted through the shaft u<3> secured to the cylinder in Fig. 2.